An outboard marine engine is desired to have as small an outer profile as possible, and the projection of the intake system of the engine from the outer profile of the outboard marine engine is therefore desired to be minimized.
However, the intake tube needs to have a certain length to maximize the intake inertia effect as a measure to improve the performance of the engine, and a surge tank having a relatively large volume needs to be placed in a part of the intake manifold, where the intake tubes leading to different cylinders merge, to prevent interferences between different cylinders. Thus, the intake system tends to take up a substantial space when the performance of the engine is desired to be improved, and the intake system has been a major factor in preventing a compact design in outboard marine engines.
Japanese patent laid open publication (kokai) No. 4-295170 discloses an arrangement in which the intake tubes extend over the axial length of the cylinders, and a surge tank integrally formed with the intake tubes is secured to a side of the cylinder block by using threaded bolts.
However, the cylinder head, cylinder block and crank case are formed separately, and the flange surface of the intake ports of the engine and the outer surface of the crank case are normally located on different planes. Therefore, the surge tank integrally formed with intake tubes is required to have two separate mounting surfaces, and ensuring the positional precision of the two mounting surfaces with respect to the corresponding mounting surfaces on the cylinder head and the cylinder block presented a major problem. This fact also caused an additional difficulty in assembling the surge tank and intake tube assembly to the engine main body.